1. Field of the Invention
The present invention relates generally to a circuit for supplying positive and negative voltages and, more particularly, to a power supply circuit to supply positive and negative power-source voltages derived from a single positive or negative voltage source.
2. Description of the Prior Art
In audio equipment, such as systems for reproducing stereophonic sound signals recorded on records, discs, or tapes, positive and negative power source voltages are often used with the intention of increasing the dynamic range of the audio output signals, for suppressing noise in the audio output channels, and for reducing the absolute values of the power source voltages in the system. These positive and negative power source voltages are generally required to have substantially the same absolute values and, therefore, the power source employed in the audio apparatus using positive and negative power source voltages must be capable of producing and supplying positive and negative voltages having the same values.
There has been proposed a power supply circuit that supplies positive and negative power-source voltages derived from two batteries, or sets of series-connected batteries, having a positive terminal grounded and a negative terminal grounded, respectively. In such power supply circuit as previously proposed, however, there are inherent problems and disadvantages involved, for example, multiple batteries are required and this involves a relatively large space requirement in the apparatus and also increases the weight of the entire system.
There has also been proposed a power supply circuit that uses a single DC voltage source to provide the required positive and negative voltages of the same value and employs a DC-DC convertor, operating with a DC voltage supplied from a single DC voltage source. Such power supply circuit also has disadvantages in that the DC-DC convertor must be constructed using: a transformer, a switching circuit connected to the primary of the transformer, a control circuit to control the operation of the switching circuit, and two detecting circuits connected to the secondary of the transformer, in order to produce the positive and negative DC voltages of the same absolute value. Thus, it is seen that the configuration of the entire power supply circuit becomes complicated and must be constructed on a relatively large scale. Additionally, further problems are involved because it is difficult to increase the efficiency in converting positive and negative DC voltages supplied from a single DC voltage source, and also it is easy to overload the switching device in the switching circuit portion of this known power supply circuit.